1. Field of the Invention
The present invention relates to a method for treating particulate material having a bulk density of about 10 lbs./cu. ft. or less with the treating agent in a continuous manner. More particularly the present invention relates to a method comprising contacting the material having a bulk density of about 10 lbs./cu. ft. or less with the treating agent as the material is being transferred into a vessel and heating the treating agent contacted material in the vessel if necessary.
2. Background
Materials having a bulk density of about 10 lbs./cu. ft. or less are commonly employed as fillers or reinforcing agents to improve the physical properties of compositions including rubbers, coatings, adhesives, paints, and sealants. Examples of these materials include, but are not limited to, fumed silicas, precipitated silicas, fumed aluminas, carbon blacks, and aerogels
It is often desirable to treat these materials having a bulk density of 10 lbs./cu. ft. or less to change their properties to render them more suitable for a particular purpose. Generally known treating agents include, but are not limited to, liquids, vapors, atomized liquids, particulate solids etc. Generally, materials having a bulk density of about 10 lbs./cu. ft. or less are treated with a treating agent in a ratio of about 1-5 parts, by weight, material, to 1 part, by weight, treating agent.
For example, for many applications it is desirable to employ a hydrophobic filler or reinforcing agent. Thus if the material having a bulk density of about 10 lbs./cu. ft. or less is normally hydrophilic, it must be treated to be made hydrophobic. As previously discussed, generally hydrophilic materials having a bulk density of 10 lbs./cu. ft. or less are treated with treating agents to make them hydrophobic. Examples of these treating agents include, but are not limited to, silicone oils, silane oils, dimethylsiloxane oils, and hydrogen fluoride vapors.
Generally about 1-5 parts, by weight, of the material having a bulk density of 10 lbs./cu. ft. or less are treated with 1 part, by weight, treating agent. For example, in an embodiment of the present invention for treating fumed silica with a silane oil, about 2-5 parts by weight fumed silica are treated with 1 part, by weight, silane oil.
As previously discussed, one example of a material having a bulk density of 10 lbs./cu. ft. or less is fumed silica. This material, also known as pyrogenic silica, is a well known reinforcing agent or filler commonly employed to improve the physical properties of compositions including silicone rubbers, coatings, adhesives, and sealants. Fumed silica basically comprises finely divided silicon dioxide particles and generally has a bulk density of about 5 lbs./cu.ft. or less and a surface area generally between about 50-400 sq.m/g.
Another example of a material having a bulk density of 10 lbs./cu. ft. or less is precipitated silica. Precipitated silica is also a well known reinforcing agent or filler commonly employed to improve the physical properties of compositions including silicone rubbers, coatings, adhesives, and sealants. Precipitated silica basically comprises finely divided silicon dioxide particles and generally has a bulk density of about 10 lbs./cu. ft. or less. For certain applications it is desirable to employ hydrophobic fumed silicas. Generally hydrophilic fumed silica is made hydrophobic by treating the hydrophilic fumed silica with a treating agent. For example U.S. Pat. No. 4,307,023 to Ettlinger et. al. discloses treating fumed silica with organosilicon compounds such as silicone oils to make the fumed silica hydrophobic and U.S. Pat. No. 4,054,689 to Calvin discloses treating fumed silica with hydrogen fluoride vapors to make the fumed silica hydrophobic. Heat may be required to facilitate a reaction between the fumed silica and the treating agent.
Generally the fumed silica is treated in a batch-type process in a vessel by filling the vessel with fumed silica and then contacting the fumed silica with a treating agent. This method is disclosed in U.S. Pat. No. 4,307,023. Mechanical mixing means may be employed to mix the fumed silica and the treating agent. The vessel may also be heated during this process. A similar process is also disclosed in U.S. Pat. No. 4,780,108 to Razzano which discloses placing a low bulk density material in a mixing vessel and then spraying a treating agent onto the material while it is being turbulently mixed. A batch-type method is also disclosed in U.S. Pat. No. 4,054,689 although in the method disclosed in U.S. Pat. No. 4,054,689 the treating agent may be added to the vessel before the fumed silica.
However these methods for treating a material having a bulk density of about 10 lbs./cu. ft. or less with a treating agent by contacting the material with the treating agent in a vessel have many disadvantages. First these methods are not continuous. To maintain the desired ratio of the material having a bulk density of about 10 lbs./cu. ft. or less to treating agent a fixed amount of both must be added to the vessel. Then the final product must be completely removed from the vessel and the vessel cleaned. Then the process starts over again with new quantities of material having a bulk density of about 10 lbs./cu. ft. or less and treating agent.
Another disadvantage with the generally employed methods is that the means for adding the treating agent to the vessel frequently clog. For example, generally the treating agent is added to the vessel through injection means or other openings at the end of a pipe or pipes. These injection means or openings can become clogged by the material having a bulk density of about 10 lbs./cu. ft. or less and therefore require frequent cleaning.
Further, in view of the fact that generally known processes are batch-type processes, there is a tendency for the treating agent to ball up in the vessel or collect on the injection means or opening. Both the injection means or opening and the vessel must therefore be cleaned to remove the treating agent balls and collected treating agent.
Also, if the vessel is heated, the treating agent balls and/or the treating agent collected on the nozzle or opening can cause fires in the vessel. These fires may also occur if excess treating agent is not thoroughly cleaned from the vessel.
Another problem with treating a material having a bulk density of about 10 lbs./cu. ft. or less with a treating agent by contacting the material with the treating agent in a vessel is ensuring all of the material is contacted by the treating agent. As previously discussed, mechanical mixing means are often employed to attempt to thoroughly contact all the material having a bulk density of about 10 lbs./cu. ft. or less with the treating agent. However, because of its density, a material having a bulk density of about 10 lbs./cu. ft. or less is difficult to move and/or agitate by mechanical means. Therefore the material located closer to the point where the treating agent is added will tend to be contacted with too much of the treating agent. Conversely, the material located further away from the point where the treating agent is added will tend to be contacted with too little treating agent. Both the "over-contacted" material and the uncontacted material end up lowering the final product's quality.
Accordingly, one object of the present invention is to overcome the disadvantages of known methods for treating a material having a bulk density of about 10 lbs./cu. ft. or less with a treating agent.
Another object of the present invention is to provide a continuous method for treating a material having a bulk density of about 10 lbs./cu. ft. or less with a treating agent.
A further object of the present invention is to provide a method for treating a material having a bulk density of about 10 lbs./cu. ft. or less with a treating agent which substantially reduces the chances of fires. A still further object of the present invention is to provide a method for treating a material having a bulk density of about 10 lbs./cu. ft. or less with a treating agent in which the material is uniformly and thoroughly contacted by the treating agent.
A still further object of the present invention is to provide a method for treating a material having a bulk density of about 10 lbs./cu. ft. or less with a treating agent which does not require frequent cleaning of the means for treating.
Other objects and advantages of the present invention will become apparent in the following description of the invention.